In some wells, due to relatively low formation gas pressures and/or other conditions, oil, water, and/or other fluids tend to accumulate at some level within the well casing rather than flowing naturally to the surface. Although various types of systems have been used for lifting and removing fluids from such wells, plungers offer particular advantages. By lifting and removing fluid from the well, a plunger can operate to increase gas production by reducing the amount of fluid pressure head acting on the formation. Alternatively, swabbing systems and rod pumps can be used in some cases to achieve similar results, but generally are not as cost effective.
Various types of plunger devices are known in the art. By way of example, one common type of plunger comprises: an elongate housing assembly; one or more external sealing devices which can be actuated to sealingly contact the interior wall of the well casing; a flow passage extending through the housing assembly; and a valve for opening and closing the flow passage.
When using a well plunger, a lubricator assembly is typically installed above ground at the wellhead for receiving and retaining the plunger between production cycles. At the beginning of a production cycle, the plunger is dropped from the lubricator assembly with the plunger valve in open position. The fluid in the well casing or tubular is thus allowed to flow through the interior flow passage so that the plunger will drop through the fluid to a stop structure installed at a desired downhole position.
The plunger will typically be configured such that, upon striking the downhole stop structure, the plunger valve will automatically close and the external seal(s) will be urged into contact with the interior wall of the casing. With the casing sealed in this manner, the pressure beneath the plunger will eventually increase to the point that the plunger will begin to rise, thus lifting the column of fluid on top of the plunger toward the surface and into an overhead production line.
In many cases, because of any one of or a combination of factors such as, for example, a further deterioration in well gas pressure, damage to the well casing, the presence of obstructions within the casing, the use of a deviated or horizontal casing having non-vertical and/or non-linear sections, the presence of multiple producing zones, the absence of casing extending entirely to the bottom of the well (e.g., in an open hole completion), and/or other formation or casing conditions, plungers and other devices either cannot be used or are of limited effectiveness for removing fluid from the well.
One example of a situation where a plunger can no longer be used is where the formation conditions have become such that fluid is now standing at a level below or at some intermediate point within a perforated section of the casing. Consequently, if a plunger were dropped into the well casing below the liquid level, and even assuming that the gas pressure in the well would otherwise be sufficient to lift the plunger, the presence of casing perforations at an elevation above the plunger would prevent the plunger from operating to raise a column of fluid to the surface.
A similar situation can also arise in the case of well casings having a plurality of perforated sections which are spaced apart vertically in different formation zones. In such cases, plungers are ineffective for removing liquid from the well if the liquid level is standing in or below one or more of the upper perforated sections. Moreover, even in cases where a small amount of fluid can be removed from a point above the top perforated zone, the pressure head conditions acting on the lower zone(s) can be such that the production from the lower zone(s) becomes blocked or is at least compromised.
Another situation which can prevent or at least create problems for the use of plungers, swabbing devices, rod pumps, and similar devices arises where the casing becomes damaged at a location above the perforated section(s). If the casing is damaged in such a way as to form one or more holes in the casing, then the operation of a plunger can be prevented or compromised in the same manner as discussed above. Alternatively, or in addition, the formation of jagged or rough areas as a result of casing damage can block the passage of a plunger or other device, or can damage or destroy the device during operation.
Another situation where the use of a plunger or similar device can be prevented or compromised is where an obstruction is present. Examples of common obstructions include, but are not limited to, (a) permanent packers and other tools which, for whatever reason, are set in the casing at problematic locations above the perforated zone(s), (b) smaller diameter liners which have been installed in the casing for repair or other reasons, (c) tapered or stepped casing sections which produce changes in the interior diameter, and (d) curved or other non-linear sections of casing of the type employed, for example, in deviated or horizontal wells.
Consequently, a need exists for an apparatus and method which will operate in situations and scenarios of the type described above to raise fluid in a well to a higher cased elevation to allow the fluid to be reached and removed by a plunger, swabbing device, rod pump, or similar device. Such apparatus and method will preferably be effective, for example, for raising a fluid (a) from a depth below a liquid level in the well casing, (b) from a depth within or below one or more perforated casing sections, (c) from a depth or location beyond a casing obstruction and (d) from a non-cased terminal portion of a well (such as, e.g., in an open hole completion). In addition, a need exists for an apparatus and system of this type which, if desired or necessary, can be conveniently installed in the well casing without requiring that tubing rigs or similar systems and equipment be transported to and used at the well site.